1. Field of the Invention
The present invention relates to semiconductor integrated circuits and, in particular, to a method of fabricating an N+ polysilicon-to-N+ silicon capacitor structure utilizing a high-energy, high-dose phosphorous implant to form a high-quality interplate dielectric which is grown simultaneously with gate oxide in the standard CMOS process flow. The resulting capacitor exhibits high capacitance per unit area and a low voltage coefficient of capacitance.
2. Discussion of the Prior Art
Integrated capacitors are key elements of advanced analog complimentary-metal-oxide-semiconductor (CMOS) integrated circuits, particularly in the areas of analog-to-digital (A/D) converters and switched capacitor filters.
Various capacitor structures have been used in analog CMOS IC devices.
Metal-to-metal and polysilicon-to-metal capacitors are described by D. Brown et al, "Advanced Analog CMOS Technology", IEDM 1985, p. 260. A poly-to-poly switched capacitor structure is described by P. Shah et al, "High Performance CMOS Technology for Telecommunications and Linear Circuit Applications", proceedings of the Custom Integrated Circuit Conference, Rochester N.Y. 1983, p. 51. Poly-to-silicon capacitor structures are described by McReary, "Matching Properties, and Voltage and Temperature Dependance of MOS Capacitors", IEEE Journal of Solid-State Circuits, Vol. SC-16, No. 6, Dec. 1981, p. 608.
Each of these capacitor structures has its own advantages and disadvantages. The selection of capacitor structure is generally based upon several criteria such as high value of capacitance per unit area, low voltage coefficient of capacitance and the process simplicity with which the capacitor structure can be fabricated.
In the past, one of the major disadvantages associated with the utilization of poly-to-silicon capacitors in an analog CMOS process has been the additional process complexity required to fabricate the capacitors. Specifically, because of the different characteristics required for the gate oxide of the MOSFET devices in the circuit and for the interplate dielectric oxide of the capacitors, it has been necessary to grow these two layers independently.